machine control interface—Pursuit control

0005-1098/79/1201-0683 $02.0010

Autonu~rica, Vol. 15, pp. 683 686 Pergamon Press Ltd. 1979. Printed in Great Britain © International Federation of Automatic Control

Brief Paper The M a n / M a c h i n e Control Interface Pursuit Control* R. WADE ALLENt and DUANE McRUERt Key Word Index

Automobiles; display systems; man-machine systems; models.

Krendel, 1974) shows the general pathways required to describe human behavior as a controller operating on visually sensed inputs and communicating with a controlled element via a manipulative output (McRuer and Krendel, 1974; Weir and McRuer, 1970). This formulation emphasizes internal signal organization as reflected by specific behavior induced by a specific control environment. The Fig. 1 system allows three different modes and control. The simplest is compensatory, in which the human controller acts in response to errors and/or controlled element output quantities. Using this pathway the operator can exert continuous closed-loop control over the controlled element so as to minimize system errors in the presence of command and

A ~ t r a e t - - M a n / m a c h i n e control interface descriptions are complicated by the versatility of the human controller as an information processing device. System input interface characteristics can lead to control behavior ranging from open-loop (precognitive), through combination open-loop, closed-loop (pursuit), to closed-loop (compensatory) control structures. The pursuit scenario described here uses driving as an instance of preview, and finds that nearly ideal open-loop control combined with a compensatory (error-correcting) system is achieved. A new concept is presented for determining certain conditions under which pursuit behavior can be effectively achieved by the human operator in a manual control system.

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FIG. 1. Major pathways involved in the man/machine interface.

Introduction

disturbance inputs. Compensatory behavior will be present when the commands and disturbances are random-appearing and the system errors are the only sources of information available. When the command inputs can be distinguished from system outputs by virtue of the display (e.g. i and rn shown separately relative to a reference) or preview (e.g. as in following a curved roadway) the pursuit pathway joins the compensatory. This new pathway provides control behavior related to the system input in conjunction with closed-loop error-correcting actions. The quality of the control can thus be, in principle, much superior to that where compensatory acts alone. When familiarity with the controlled element dynamics and the perceptual field is achieved, the operator can exert precognitive control. This behavior results in neuromuscular commands which are programmed in an open loop fashion to achieve desired controlled element motions. These commands are selected from a repertoire of previously learned control

THE HUMAN controller is a combination of sensing, computation, and actuating elements. "Computation' includes the arrangement of internal signal processing pathways, functional operations on internal signals, and reconfiguration of pathways and functional operations as the situation changes (i.e. adaptation). Figure 1 (McRuer and

*Received September 25 1978; revised May 8 1979. The original version of this paper was presented at the 7th IFAC Congress on A Link Between Science and Applications of Automatic Control which was held in Helsinki, Finland during June 1978. The published Proceedings of this IFAC Meeting may be ordered from: Pergamon Press Ltd., Headington Hill Hall, Oxford, OX3 0BW, U.K. This paper was recommended for publication in revised form by associate editor B. Gaines. tSystems Technology, Inc. Hawthorne, California, U.S.A. 683

684

Brief Paper

movements, and are conditioned responses which may be triggered by the situation and the c o m m a n d and control quantities, although they are not continuously dependent thereon. Like the pursuit pathway, precognitive control often appears in company with the compensatory operations as a dual-mode control a form where the control exerted is initiated and largely accomplished by the precognitive action but may be finished with compensatory error-reduction operations. The compensatory subsystem of the operator has been extensively studied using a control theory perspective for over three decades. A very broad experimental data base exists IMcRuer and Krendel, 1974: Sheridan and Ferrell, 19741 and an extensive manual control theory has been developed using modifications to: conventional feedback analysis techniques: parameter optimization with fixed-form procedures; and quadratic optimal control theory (McRuer and Krendel, 1974; Sheridan and Ferrell, 1974; Kleinman, Baron and Levison, 1970, 197I). For most practical concerns related to man/machine control interfaces there are no further critical research issues for compensatory operations. It is in transition from the domain of research to that of routine applications. Precognitive behavior has been studied to a much lesser extent. A variety of research studies have demonstrated time optimal control behavior in the well trained h u m a n operator, however (McRuer and Krendel, 1974; Smith, 1962; McRuer and co-workers, t968; Miller, 1969; Jagacinski, Burke and Miller, 1976). More recently, dual mode precognitivecompensatory behavior has been demonstrated in automobile maneuvering (e.g. McRuer and co-workers, 1977). Pursuit control behavior is probably least understood human controller mode, and research has often given ambiguous results. As reviewed by McRuer and Krendel (1974) some studies comparing compensatory and pursuit systems have revealed distinct pursuit behavior, while others show minimal differences, and sometimes even degraded performance when display information was provided to allow for pursuit control. Below, we consider pursuit control in more detail. Recent driving simulation results are analyzed from a pursuit control point of view and certain conditions are hypothesized for displayed control cues which make them particularly adwmtageous in evoking productive pursuit behavior. Pursuit

systems

In the situation where pursuit behavior is present the system appears as in Fig. 2 with only t~, and Yp, blocks operating. The relationships between input and output, and input and error are s , 1 + Vp, Y,

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where YtJ represents an "equivalent" set of open-loop operator/controlled-element dynamics which arc influenced as shown by the pursuit feedforward operation Yp; In many experimental situations it is not known whether pursuit behavior (i.e. I'), ~()) is truly present. It can, however, bc readily assessed t~y examining the form of Yt~,and this is often the experimental procedure adopted. Subject to the constraints imposed by stabilization of the controlled element, one would like Y, to be very large so that I,n/il~l and je/ij-,0. This can be accomplished if the pursuit pathway is adjusted so that Ypy~±l. Increasing the compensatory characteristics Y~, to achieve the same end would lead to destabilization of [he control loop. For Yp to be calibrated to Y,., functional knowledge of Y,. would hav'e to be in "memory', which can be evolved with experience. There have been extensive studies of pursuit behavior as induced by pursuit displays of the kind shown in Fig. 3. For

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e(t) : m(t)- i(t) lqG. 3. Pursuit display. those with Y,.-Kc and Y~=Kc/s2, the desirable feature YpY,,±I was approximated (Wasicko, McRuer and Magdaleno, 1966). However, for the controlled element Kc/s, Wasicko, McRner and Magdaleno (1966); Allen and Jex (1968); and Reid (1969t have indicated that the influence of the Yp, feedforward was negligible in the control. In other words, there was very littlc cognitive difference between a physical compensatory and physical pursuit display for this controlled element as reflected in Y/~ or, for that matter, direct Yp, measurements. This state of affairs has led to some confusion about the nature of pursuit control and, in particular, the conditions under which it might be generated. However, a recent series of driver/vehicle control experiments has shed a good deal of light on this matter (Allen and co-workers, 1977). The experiments of interest involve driver control of an automobile's lateral position. This is a multiloop task in which the driver uses lateral deviation in the lane and vehicle heading as compensatory feedbacks. In principle, the driver could improve path guidance by making use of path command information in the visual field, such as road curvature, by operating in a pursuit mode. If, for instance, the driver directly perceived the required path curvature in terms of a

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Brief Paper

685

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FIG. 4. Pursuit operations in driver/vehicle system with preview.

pure gain feedforward, then the driver/vehicle control system would appear as in Fig. 4. The car dynamics relating yawing velocity, r, to the steering wheel deflection are given approximately by r

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where Uo is car speed and I is the wheelbase. The compensatory loop is adjusted so that the car's lag, T,, is approximately offset by the driver lead, Tt. The curvature of the car's path is given by heading rate divided by speed (r/Uo) or C u r v a t u r e ~ _ 6 ~ / l . Therefore, if perceived curvature is used as a pursuit pathway, K~ would be adjusted such that u0g, ---=1. I

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A simulation experiment using a fixed-base simulator and a complete line-drawn roadway display (Allen, Hogge and Schwartz, 1977) employed wind disturbances with a straight roadway to exhibit compensatory-alone characteristics and road curvature c o m m a n d s to determine if the pursuit pathway was energized. With the wind disturbances and straight road, the driver is not aware of the input until the car responds. The road curvature input, on the other hand, is directly perceivable by the driver through preview. Measurements of effective open heading loop describing functions were made as described by Allen and co-workers (1977). These a m o u n t to Yp measurements. Typical results from the simulation experiment are illustrated in Fig. 5. The describing function data show that for pursuit path c o m m a n d driving the Y/~ is indeed larger than that for the wind gust compensatory regulation task. The solid and dashed lines are not data fits but rather model descriptions in terms of the Fig. 4 model in which the terms K~., K~, K,, etc., were found using an optimal identification routine. The models clearly do a reasonable job of matching the system data. An important part of all of this for the current discussion is how closely the idealized relationship of equation (5) is approached. The above tests were performed at a fixed speed of 3 0 m p h (44ft/sec) and a simulated wheel base of 9.25ft. Using these numbers in equation (5) yields a desirable K, value of about 0.210 for good pursuit behavior, which compares favorably with the measured value of 0.176 given in Fig. 5. Other test conditions have given even closer comparison, while measurements under severe visibility reduction have shown that pursuit behavior deteriorates with reduced preview due to restriction of visual curvature cues (Allen and coworkers, 1977).

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FIG. 5. Driver equivalent open-loop describing functions. The above car driving experiment and reconsideration of other past research has led to the following explanation for complex visual field situations if they are to provide ideal pursuit behavior. In essence, the operator must be able to perceive directly an input quantity in the complex surround which allows a pure gain feedforward transfer function. In the car example, since r

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6w then steering wheel deflections proportional to perceived road curvature will roughly cancel the road curvature command. The above considerations are summarized in Fig. 6.

Brief Paper

686

ReJerences

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Concluding remarks A particularly interesting aspect of the above discussion is that pursuit operations are potentially available on a number of system c o m m a n d input variables. The one selected by the operator is intrinsically the simplest and most parsimonious, i.e. that roadway attribute which permitted the pursuit transfer characteristics to be a pure gain. If a good curvature cue were not present, the development of a pursuit pathway proportional to the second derivative of roadway position or the derivative of roadway heading would conceivably be adequate. These, however, would presumably incur an increased time delay penalty, due to additional mental processing requirements, and hence would not be as desirable. To the extent that these results can be generalized, the best way to induce pursuit behavior is to have presented in the surround or display those c o m m a n d input quantities which arc proportionally related to an output so that Yp can be a pure gain. Further, sufficient preview or its equivalent must bc present to permit the utilization of the pathway itself.

Allen, R. W., J. R. Hogge and S. H. Schwartz (1977). A simulator for research in driver, vehicle and environment interaction, presented at the 56th Annual Meeting of the Transportation Research Board, Washington, D.C. Allen, R. W. and H. R. Jex (1968). An experimental investigation of compensatory and pursuit tracking displays with rate and acceleration control dynamics and a disturbance input, NASA CR-1082. Allen, R. W., and co-workers (1977). Drivers' visibility requirements for roadway delineation. Vol. 1: effects of contrast and configuration oil driver performance and behavior. Federal Highway Administration RD-77-165. Jagacinski, R. J., M. W. Burke and D. P. Miller (1976). Time optimal control of an undamped harmonic oscillator: evidence fur biases and schemata. In 12th Ann. Conf. on Manual Control, NASA TM X-73, 170, pp. 383 405. Kleinman, D. L., S. Baron and W. H. Levison (1970). An optimal control model of h u m a n response, Parts I and 2. Automatica 6 (3). Kleinman, D. I,., S. Baron and W. H. Lcvison {1971). A control theoretic approach to manned-vehicle systems analysis. IEEE Trans. AC-16(6) 824 832. McRucr, D. T., R. W. Allen, D. H. Weir and R. I1. Klcm (19771. New results in d i n e r steering control models. lluman Factors 19(4), 381 397. McRuer, D. T., L. G. Hofmann, H. R. Jex and co-workers (1968). New approaches to human-pilot/vehicle dynamic analysis, AFFDL-TR-67-t 51). McRuer, 1). T. and E. S. Krendcl (1974). Mathematical models of h u m a n pilot bellavior, AGAR Dograph t88. Miller, Duncan C. (1969). Behavioral sources of suboptimal h u m a n performance in discrete control tasks, Mlq Engineering Projects Lab., DSR 70283+9, Ph.D. Thesis. Reid, I.. 1)+ (1969). The measurement of h u m a n pilot dynamics in a pursuit-plus-disturbance tracking task. l~oronto, Can., Univ. of Toronto, Inst. for Acrnspacc Studies, Rept. 138. Sheridan, T. B. and W. R. Fcrrell (1974). Man-Machine Systems: Injormation, Control, aM Decision Models of ttuman Pe(/brmance. MIT Press, Mass., 15.S.A. Smith, O. J. M. (1962). Nonlinear Computations m the H u m a n Controller, IRE 7?ans. BME-9(2), 125 128. Wasicko, R..I., D. T. McRuer and R. t!. Magdalcno (1966). Iluman pilol dynamic response in single-loop systems with compensatory and pursuit displays, AFFI)L-TR-66-137. Weir, I). H. and D. T. McRuer (197(1). I)ynamics of driver/ vehicle steering control. Automatica, 6(I) 87 9g.